This invention relates in general to techniques for efficiently employing the hardware and software in a data processing system. More particularly, this invention is directed to time division multiplexing techniques for employing the address bus.
Data processing systems are known, often of a self-contained hand held variety, in which a central processing unit (CPU) responds to keyboard inputs and reads from a read only memory (ROM) to provide appropriate data and information to a random access memory (RAM) unit thereby temporarily storing information to be displayed on a display screen associated with the keyboard.
It is known in such arrangements to provide certain processes for speeding up the response time between a keyboard input and the display of appropriate information on the screen. One technique that is employed is to provide direct memory access (DMA) hardware designed to transfer information from the RAM unit to the screen without requiring use of the CPU for that function.
It should be understood that techniques of speeding up processing are part of a trade-off between CPU capacity, hardware costs and response time. In order to provide compact, relatively inexpensive data processing units and in particular those that are self-contained, battery operated, hand-held units, it is important that the most efficient use of hardware and software be employed so that cost and size can be minimized while response time can be maintained at a level acceptable to the user.
Accordingly, the major purpose of this invention is to provide various techniques for more efficiently using the equipment in a data processing system having a keyboard and a display screen.